Triisopropylphenylsulfonyl azide

Diazo transfer from 2,4,6-triisopropylphenylsulfonyl azide to the enolate derivatives of hindered cyclic ketones can be achieved by using phase transfer conditions Lombardo, L. Mander, L. N. Synthesis 1980, 368. 

Proton removal from tetralone (47) is the limiting factor and the diazo transfer is carried out using the reactive azide triisopropylphenylsulfonyl azide (46) (TPPSA).19... 

C-Formylation or a-oximation of the highly hindered a-methylene group in the parent ketone is not possible. Direct transfer of the diazo group from tosyl azide under phase transfer conditions has been found unproductive.19 A variety of highly hindered ketones are converted to corresponding diazo ketones with 2,4,6-triisopropylphenylsulfonyl azide under phase-transfer conditions.19 Tetrabutylammonium bromide and 18-crown-6-ether are used as catalysts in these diazo transfer reactions. This method is superior to C-nitrosation followed by diazotization with chloramine. The diazo compounds 66 (55%) and 68 (72%) are obtained using this method. 

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